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cmd/compile: suppress typecheck errors in a type switch case with broken type

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If a type switch case expression has failed typechecking, the case body is
likely to also fail with confusing or spurious errors. Suppress
typechecking the case body when this happens.

Fixes #28926

Change-Id: Idfdb9d5627994f2fd90154af1659e9a92bf692c4
Reviewed-on: https://go-review.googlesource.com/c/158617
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
This commit is contained in:
Gergely Brautigam 2019-01-18 21:43:56 +01:00 committed by Daniel Martí
parent 9cb2471334
commit 8ee9bca272
2 changed files with 32 additions and 8 deletions
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16
src/cmd/compile/internal/gc/swt.go
View File

@ -184,18 +184,11 @@ func typecheckswitch(n *Node) {
}
}
if n.Type == nil || n.Type.IsUntyped() {
// if the value we're switching on has no type or is untyped,
// we've already printed an error and don't need to continue
// typechecking the body
return
}
if top == Etype {
ll := ncase.List
if ncase.Rlist.Len() != 0 {
nvar := ncase.Rlist.First()
if ll.Len() == 1 && ll.First().Type != nil && !ll.First().Type.IsKind(TNIL) {
if ll.Len() == 1 && (ll.First().Type == nil || !ll.First().Type.IsKind(TNIL)) {
// single entry type switch
nvar.Type = ll.First().Type
} else {
@ -203,6 +196,13 @@ func typecheckswitch(n *Node) {
nvar.Type = n.Type
}
if nvar.Type == nil || nvar.Type.IsUntyped() {
// if the value we're switching on has no type or is untyped,
// we've already printed an error and don't need to continue
// typechecking the body
continue
}
nvar = typecheck(nvar, ctxExpr|ctxAssign)
ncase.Rlist.SetFirst(nvar)
}

24
test/fixedbugs/issue28926.go Normal file
View File

@ -0,0 +1,24 @@
// errorcheck
// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
type Stringer interface {
String() string
}
func main() {
var e interface{}
switch e := e.(type) {
case G: // ERROR "undefined: G"
e.M() // ok: this error should be ignored because the case failed its typecheck
case E: // ERROR "undefined: E"
e.D() // ok: this error should be ignored because the case failed its typecheck
case Stringer:
// ok: this error should not be ignored to prove that passing legs aren't left out
_ = e.(T) // ERROR "undefined: T"
}
}